titan oxit

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Synthesis and photocatalytic application of ternary Cu–Zn–S nanoparticle-sensitized
TiO2 nanotube arrays
ThanhThuy Tran.T a,b
, Pengtao Sheng a
, Chen’an Huang a
, Jiezhen Li a
, Lan Chen a
, Lijuan Yuan a
,
Craig A. Grimes c
, Qingyun Cai a,⇑
a
State Key Laboratory of Chemo/Biosensing and Chemometrics, Department of Chemistry, Hunan University, Changsha 410082, People’s Republic of China
b
Department of Chemistry, Ho Chi Minh City University of Industry, Ho Chi Minh, Viet Nam
c
Department of Chemical Engineering, Nanjing University of Technology, Nanjing 210009, People’s Republic of China
h i g h l i g h t s
" An enhanced photocatalytic activity of Cu–Zn–S/TiO2 NTAs catalyst was fabricated by pulse electrodeposition method.
" The new catalyst was successfully applied in the photodegradation of 2,4-D and 9-AnCOOH under AM1.5G illumination.
" Photoelectrocatalytic process with excellent stability was established.
a r t i c l e i n f o
Article history:
Received 1 June 2012
Received in revised form 30 August 2012
Accepted 3 September 2012
Available online 11 September 2012
Keywords:
TiO2
Nanotube
Nanotube array
Cu–Zn–S
Photocatalytic
Anthracene-9-carboxylic acid
2,4-Dichlorophenoxyacetic acid
a b s t r a c t
A novel photocatalyst is prepared by pulse-electrodeposition of ternary Cu–Zn–S nanoparticles of 2.3 eV
bandgap onto the surface of TiO2 nanotube array films. Under AM1.5G illumination the Cu–Zn–S
sensitized TiO2 nanotube arrays (Cu–Zn–S/TiO2 NTAs) exhibit a significantly increased capability for
photocatalytic degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) and anthracene-9-carboxylic acid
(9-AnCOOH). After 150 min illumination 100% of 2,4-D is removed, compared to 51.8% using the non-
sensitized TiO2 NTAs; while after 60 min illumination 100% of 9-AnCOOH is removed, compared to
68.5% using the non-sensitized TiO2 NTAs. Herein we consider synthesis details and application of the
material system.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
2,4-Dichlorophenoxyacetic acid (2,4-D) is one of the most
widely used systemic pesticide/herbicides while anthracene-9-car-
boxylic acid (9-AnCOOH) is toxic to the epithelium, inhibiting
transport, that in turn increases the permeability of the paracellu-
lar pathway. Unfortunately, due to their excellent chemical stabil-
ity it is difficult to remove 2,4-D and 9-AnCOOH from
contaminated wastewater [1–4]. Our interest is in the photocata-
lytic degradation of these agents. Among photocatalytic materials,
nano-architectured TiO2 is one of the most useful due to its low
cost, widespread availability, non-toxicity, high photocatalytic
activity, and excellent chemical stability [5–8]. However as is com-
monly known, photocatalytic application of TiO2 is limited by its
relatively large bandgap of %3.0 eV for rutile and 3.2 eV for the
anatase phases, which limits photoactivity to the ultraviolet region
[9,10]. Many studies have focused on shifting the optical response
of titania by doping with transition and/or noble metals [11,12],
nonmetals [13–15], or semiconductors [16–18]. Sensitization of
TiO2 with binary [19,20] and ternary [16,21] low bandgap semi-
conductors has attracted considerable, particularly since the
photocorrosion stability can be improved by doping or shelling
one material with another. Further, the bandgap can be tuned by
elemental doping. For example, ternary metal sulfides have excel-
lent photocorrosion stability and greater photocatalytic activity
than binary metal sulfides [22,23]. As a ternary metal sulfide,
Cu–Zn–S has a direct band gap of 2.3 eV making it well suited for
solar applications [24–27].
In this work, semiconducting low bandgap ternary Cu–Zn–S
nanoparticles are used to sensitize highly-oriented TiO2 nanotube
arrays (NTAs). Pulse electrodeposition [28] is used for deposition
1385-8947/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.cej.2012.09.004
⇑ Corresponding author.
E-mail address: qycai0001@hnu.edu.cn (Q. Cai).
Chemical Engineering Journal 210 (2012) 425–431
Contents lists available at SciVerse ScienceDirect
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3. Author's personal copy
of the Cu–Zn–S nanoparticles onto the TiO2 NTAs. Compared with
other deposition methods, such as SILAR and solution growth tech-
niques [25–27], electrodeposition allows for facile control of the
size and composition of the semiconductor nanoparticles. To the
best of our knowledge, there are no reports on sensitization of
TiO2 nanotube arrays with Cu–Zn–S nanoparticles, nor their appli-
cation to the photocatalytic degradation of organic pollutants;
herein we consider material synthesis and application to photocat-
alytic degradation of 2,4-D and 9-AnCOOH.
2. Experimental
2.1. Materials
Titanium foil (99.8% purity, 0.25 mm thick) was purchased from
Aldrich (Milwaukee, WI). 2,4-D was obtained from Shanghai
Chemical Corporation of China. 9-AnCOOH was obtained from Sig-
ma–Aldrich Chemie Inc. All other reagents of analytical grade were
obtained from commercial sources and used as received. Deionized
water was used for preparation of all aqueous solutions.
2.2. Methods
Titanium foil samples were cut into 3.5 cm  1.0 cm pieces. The
Ti foil samples were first ultrasonically cleaned in acetone and eth-
anol, each for 5 min, and then cleaned in deionized water. The
cleaned titanium pieces were anodized at a constant potential of
20 V in an electrolyte containing 0.1 M NaF and 0.5 M NaHSO4 at
room temperature for 2 h using a platinum cathode. The titania
NTAs formed on Ti substrate were then annealed in air at 500 °C
for 3 h for crystallization in the anatase phase.
Ternary Cu–Zn–S nanoparticles were pulse electrodeposited
onto TiO2 NTA samples using a three-electrode electrochemical cell
with the TiO2 NTAs, resting upon a Ti substrate, as the working
electrode, a Pt wire as the counter electrode, and a saturated calo-
mel electrode (SCE) as reference in a pH 2.5 electrolyte solution
containing CuC12 (2 mM), ZnCl2 (5 mM), and Na2S2O3 (20 mM);
solution pH was adjusted by addition of HCl solution. An ‘on’ pulse
potential of À2.0 V (vs. SCE) was applied to the cathode for 0.2 s,
followed by an ‘off’ potential of 0 V (vs. SCE) for 1.0 s. After depo-
sition, the Cu–Zn–S/TiO2 NTA electrodes were repeatedly rinsed
with deionized water. A field emission scanning electron micro-
scope (FESEM, Hitachi S-4800), and transmission electron micro-
scope operating at 200 kV (TEM-2100F; JEOL, Tokyo, Japan) was
used for studying the Cu–Zn–S/TiO2 NTA morphologies. Elemental
analyses were studied with an energy dispersive X-ray spectrome-
ter (EDX). The UV–Vis diffuse reflectance absorption spectrum was
determined using a Cary 300 Conc UV–visible spectrophotometer
with an integrating sphere.
Photoelectrochemical measurements were conducted using an
electrochemical workstation (CHI660C, Shanghai Chenhua Instru-
ment Co. Ltd.) in a standard three-electrode configuration with a
Cu–Zn–S/TiO2 NTA sample, or non-sensitized TiO2 NTA sample,
3.0 cm2
in area, as the working electrode, a Pt wire counter elec-
trode, and a SCE reference electrode. A 500 W xenon lamp (CHF-
XQ-500 W, Beijing Changtuo Co., Ltd.) was used as the light source,
filtered to 100 mW cmÀ2
AM1.5G as determined by a radiometer
(NOVA Oriel 70260). Photocatalytic activity of the Cu–Zn–S/TiO2
NTAs was evaluated by degradation of 2,4-D or 9-AnCOOH in a
quartz cell with a geometrical size of 3.5 Â 1.0 cm the reaction
solution was 20 mL, with tests carried out under stirring.
Photoelectrochemical properties were measured in 0.05 M Na2-
SO4 or 0.1 M KOH aqueous solution. Tests on the degradation of or-
ganic pollutants were performed in 20 mL 0.05 M Na2SO4 aqueous
solution containing 20 mg LÀ1
2,4-D or 9-AnCOOH; solution pH
was adjusted by addition of H2SO4 or NaOH. 2,4-D and 9-AnCOOH
concentrations, in aqueous solutions, were measured based on
their maximum absorption at 227 nm and 253 nm, respectively,
using an UV–Vis Cary 300 spectrophotometer (Varian, USA). The
absorbance A0 measured after stirring for 0.5 h in the dark was ta-
ken as the initial concentration C0 of the solution. The absorbance
At measured after variable periods of illumination was taken as
corresponding to the residual concentration Ct The degree of or-
ganic compound degradation was calculated by:
Removal efficiency ¼
ðC0 À CtÞ
C0
 100% ¼
A0 À At
A0
 100%
3. Experimental results and discussion
3.1. Characterization of the Cu–Zn–S ternary-sensitized TiO2 NTAs
Fig. 1 shows the surface morphologies of non-sensitized TiO2
NTAs and Cu–Zn–S nanoparticle sensitized TiO2 NTAs obtained by
FESEM. The TiO2 NTAs have an inner pore diameter ranging from
70 to 110 nm and wall thickness of about 15 nm (Fig. 1A). The for-
mation mechanism of the TiO2 NTAs is well documented [29,30].
Pulse-potential deposition results in the formation of Cu–Zn–S
nanoparticles on the surface of the TiO2 NTAs as shown in Fig. 1B
and C. The particle density increases with increasing number of
deposition cycles. TEM analysis, Fig. 1D, shows the particle size is
around 30 nm. As shown in Fig. 1E, the Cu–Zn–S nanoparticles ap-
pear primarily distributed on the top surface of the TiO2 NTAs. Com-
position was determined by EDX spectroscopy, Fig. 1F; the
calculated molar percentages of Cu, Zn, and S are about 0.048%,
0.047%, and 0.099%, respectively, corresponding to the molar ratio
of 1:1:2. UV–Vis diffuse reflectance spectra is shown in Fig. 2; char-
acteristic absorption peaks of non-sensitized TiO2 NTAs present in
UV region which result from the absorption of the trapped holes
[31], while sensitization of TiO2 NTAs samples with Cu–Zn–S nano-
particles results in a red shift of the absorption peaks. The narrow
band-gap of Cu–Zn–S ternary is responsible for the improved
absorption capability of TiO2 NTAs in the visible-light region.
3.2. Photoelectrochemical properties of the Cu–Zn–S sensitized TiO2
NTAs
Fig. 3A shows the photocurrent response of TiO2 NTAs and
Cu–Zn–S/TiO2 NTAs samples in a 0.05 M Na2SO4 solution under
AM1.5G illumination. Samples Cu–Zn–S sensitized with (a) 10 cy-
cles, (b) 100 cycles, (c) 5 cycles, and (d) 300 deposition cycles show,
respectively, measured photocurrent densities of 1.65 mA cmÀ2
,
1.56 mA cmÀ2
, 1.47 mA cmÀ2
, and 1.27 mA cmÀ2
, while that of
the non-sensitized TiO2 NTAs sample (e) is 0.81 mA cmÀ2
. Dark
photocurrents of all samples are near zero. Maximum photocurrent
density is achieved with 10 deposition cycles; it appears too little
Cu–Zn–S deposition results in poor light absorption, while too
much Cu–Z–S deposition blocks the nanotube array pores hinder-
ing separation of the photogenerated charge.
Photocurrent density–voltage (J–V) characteristics of the sam-
ples were investigated in 0.1 M KOH electrolyte to further examine
photoelectrochemical properties, Fig. 3B. Sample photocurrents
gradually increase with increasing applied potential, with increas-
ing potential promoting separation of the photo-generated charges
[32,33]. Under 0.5 V bias (vs. SCE) the photocurrent density of the
10 deposition cycle Cu–Zn–S/TiO2 NTAs electrode is 2.6 times that
of the non-sensitized TiO2 NTAs sample. A more negative zero-cur-
rent potential represents superior separation efficiency of the
photogenerated electrons and holes [34]; the zero-current poten-
tial of the 10 cycle sample is À0.92 V, compared to that of both
the 100 cycle and 300 cycle samples with a zero-current potential
of À0.88 V.
426 ThanhThuy Tran. T et al. / Chemical Engineering Journal 210 (2012) 425–431

4. Author's personal copy
3.3. Photocatalytic degradation of organic pollutants
Fig. 4A shows the effect of pH on the degradation of a 20 mg LÀ1
2,4-D solution after 2.5 h irradiation with the (10-cycle deposited)
Cu–Zn–S/TiO2 NTAs as the catalyst. The degradation efficiency of
2,4-D is of 53.3%, 72.9%, 100%, 62.3%, 55.2%, and 32.6% at pH = 1,
2, 3, 5, 7, 10, respectively.
Following the works of Serpone [35–38] we hypothesize the fol-
lowing photocatalytic degradation mechanism as illustrated in
Scheme 1:
TiO2 !
hv
TiO2ðhþ
þ eÀ
Þ ð1Þ
Cu À Zn À S !
hv
Cu À Zn À Sðh
þ
þ eÀ
Þ ð2Þ
Cu À Zn À Sðh
þ
þ eÀ
Þ þ TiO2ðhþ
þ eÀ
Þ
! Cu À Zn À Sðh
þ
þ hþ
Þ þ TiO2ðeÀ
þ eÀ
Þ ð3Þ
TiO2ðeÀ
þ eÀ
Þ þ O2 ! TiO2 þ Å
OÀ
2 ð4Þ
Å
OÀ
2 þ Hþ
HOÅ
2 pKa ¼ 4:88 ð5Þ
2HOÅ
2 ! O2 þ H2O2 ð6Þ
H2O2 !
hv
2Å
OH ð7Þ
Cu À Zn À Sðh
þ
þ hþ
Þ þ H2O ! Cu À Zn À S þ Å
OH þ Hþ
ð8Þ
Cu À Zn À Sðh
þ
þ hþ
Þ þ OHÀ
! Cu À Zn À S þ Å
OH ð9Þ
CuZnS2 NPs
CuZnS2 NPs
(B)(A)
(D)(C)
(F)(E)
Fig. 1. FESEM top-surface images of: (A) non-sensitized TiO2 nanotube arrays; (B) TiO2 nanotube arrays sensitized with 10 Cu–Zn–S deposition cycles; (C) TiO2 nanotube
arrays sensitized with 300 Cu–Zn–S deposition cycles; (D and E) TEM images and (F) EDS spectrum of Cu–Zn–S sensitized TiO2 nanotube arrays.
Fig. 2. UV–vis diffuse reflectance spectra of: (a) non-sensitized TiO2 nanotube
arrays film; nanotube array film sensitized with (b) 300, (c) 100, and (d) 10 Cu–Zn–S
deposition cycles.
T. Tran.T et al. / Chemical Engineering Journal 210 (2012) 425–431 427

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Å
OH þ organic pollutants ! Degradation products ð10Þ
Photogenerated electrons from the Cu–Zn–S CB transfer to the
TiO2 CB (Eq. (3)) and react with electron acceptors such as O2 dis-
solved in water, producing superoxide radical anion Å
OÀ
2 (Eq. (4))
which then combines with H+
forming hydrogen peroxide (H2O2)
(Eqs. (5) and (6)). H2O2 can be reduced to hydroxyl radicals (Å
OH)
under illumination (Eq. (7)) [35–37]. The photogenerated holes
move from the TiO2 VB to the Cu–Zn–S VB (Eq. (3)), hindering their
recombination that usually occurs in the non-sensitized TiO2, and
react with OHÀ
/H2O to form hydroxyl radicals (Å
OH) (Eqs. (8) and
(9)) [39]. The organic compounds are then degraded by ÁOH radi-
cals (Eq. (10)).
The degradation efficiency is due to the amount of ÁOH free rad-
icals, described by Eqs. (5)–(7) for an acidic solution and Eqs. (8)
and (9) for a basic solution. When the pH value is higher than
4.88, the pKa for producing HOÅ
2 free radicals, the reaction of Eq.
(5) will proceed in the reverse direction [40] to bring about a de-
crease in the mount of Å
OH (Eqs. (6) and (7)) and consequently re-
duce the degradation efficiency. Further, in high pH solutions
ionization of 2,4-D makes it negatively charged, hence the 2,4-D
anions are repulsed by Ti–OÀ
[40] in turn reducing the degradation
efficiency. When the pH is lower than 4.88 the reaction favors the
formation of HOÅ
2 free radicals that in turn produce more Å
OH free
radicals and hence increase degradation efficiency. However too
Fig. 3. (A) Photocurrent response, measured in 0.05 M Na2SO4 solution, of: TiO2 nanotube arrays sensitized with Cu–Zn–S through (a) 10, (b) 100, (c) 5, and (d) 300 deposition
cycles; (e) non-sensitized TiO2 nanotube arrays. (B) Current–voltage characteristics measured in 0.1 M KOH solution of: (a and b) non-sensitized TiO2 nanotubes arrays in the
dark, and under illumination, respectively; Cu–Zn–S sensitized TiO2 nanotube arrays of (c) 300, (d) 100, and (e) 10 deposition cycles.
Fig. 4. (A) The effect of pH on the removal of 20 mg LÀ1
2,4-D solution with AM1.5G illumination of 2.5 h; a 3 cm2
(10-cycle deposition) Cu–Zn–S /TiO2 NTAs sample was used
as the catalyst. (B) For the same catalyst, the effect of initial concentration on the photoelectrocatalytic degradation of 2,4-D performed in 20 mL aqueous solutions containing
0.05 M Na2SO4 and different initial 2,4-D concentrations from 20 mg LÀ1
to 100 mg LÀ1
under 0.5 V bias potential in 2.5 h AM 1.5G illumination. Solution pH was adjusted to 3
by addition of H2SO4 or NaOH.
h+
h+
e-e-
Cu-Zn-S Ternary TiO2
hv
hv
H+
+ .
O2
-
H2O2 OH
Organic pollutants
Degradation products
O2/
.
O2
-
e-
Scheme 1. Illustration of electron and hole transfer in the Cu–Zn–S sensitized TiO2 nanotube arrays and mechanism of photocatalysis degradation.
428 ThanhThuy Tran. T et al. / Chemical Engineering Journal 210 (2012) 425–431

6. Author's personal copy
low a OH-
concentration in a strong acidic system is unfavorable
for the formation of hydroxyl radicals, which also results in a
decrease in the degradation efficiency (Eq. (9)) [41,42]. For 9-
AnCOOH degradation the optimal pH is 5 (data not shown).
Fig. 4B shows the degradation efficiency of 2,4-D with different
initial concentrations using the (10-cycle deposited) Cu–Zn–S/TiO2
NTAs as the catalyst. The photoelectrocatalytic degradation was
performed in 20 mL aqueous solutions containing 0.05 M Na2SO4
and different initial concentrations of 2,4-D from 20 mg LÀ1
to
100 mg LÀ1
under 0.5 V bias potential in 1.5 h AM1.5G illumina-
tion. Solution pH was adjusted to 3 by addition of H2SO4 or NaOH.
The removal of 2,4-D decreases from 100% to 93.1%, 75.3%, and
54.5% when the initial concentration of 2,4-D increases,
respectively, from 20 to 30, 50, and 100 mg LÀ1
. For high initial
concentrations the 2,4-D molecules can block photons from reach-
ing the photocatalyst surface [43] resulting in a decrease in degra-
dation efficiency.
Fig. 5A shows in situ UV–vis spectra of 20 mg LÀ1
2,4-D solution
under AM1.5G illumination with the (10-cycle deposited) Cu–Zn–
S/TiO2 NTAs as the catalyst; the 20 mL solution contains 0.05 M
Na2SO4 and 20 mg LÀ1
2,4-D adjusted to pH = 3. After 2.5 h illumi-
nation all characteristic peaks of 2,4-D disappear completely indi-
cating that the 2,4-D is completely degraded. Fig. 5B shows
AM1.5G 2,4-D degradation efficiency for: (a) no catalyst, direct
photolysis; (b) photocatalysis using a TiO2 NTAs sample; (c) photo-
electrocatalytic (PEC) with a bias potential of 0.5 V (vs. SCE) using a
TiO2 NTAs sample; (d) photocatalysis using a (10-cycle deposition)
Cu–Zn–S/TiO2 NTAs sample; (e) PEC with a bias potential of 0.5 V
Fig. 5. (A) UV–Vis determination of photoelectrocatalytic decomposition of 2,4-D using (10-cycle deposition) Cu–Zn–S sensitized TiO2 nanotube arrays under AM1.5G
illumination. (B) AM1.5G decomposition of 2,4-D degradation for: (a) no catalyst, direct photolysis; (b) photocatalysis using a TiO2 NTAs sample; (c) photoelectrocatalytic
(PEC) with a bias potential of 0.5 V (vs. SCE) using a TiO2 NTAs sample; (d) photocatalysis using a (10-cycle deposition) Cu–Zn–S/TiO2 NTAs sample; (e) PEC with a bias
potential of 0.5 V (vs. SCE) using a (10-cycle deposition) Cu–Zn–S/TiO2 NTAs sample. The initial concentration of 2,4-D was 20 mg LÀ1
and the pH value was 3.
Table 1
Comparative data on the degradation efficiency of 2,4-D.
Catalyst 2,4-D concentration (ppm) Irradiation % degradation Reference
TiO2 fiber 9.67 120 min/UV light 54% Giri et al. [45]
Cu–Zn–S/TiO2 20 120 min/Solar light 90% Present study
TiO2 P-25 30 150 min/UV light 53% Galindo-Hernández et al. [46]
Cu–Zn–S/TiO2 30 150 min/Solar light 93% Present study
TiO2 P-25 50 150 min/UV light 56% Modestov et al. [47]
Cu–Zn–S/TiO2 50 150 min/Solar light 75% Present study
Fig. 6. (A) UV–Vis determination of photoelectrocatalytic 9-AnCOOH using (10-cycle deposition) Cu–Zn–S sensitized TiO2 nanotube arrays under AM1.5G illumination. (B)
AM1.5G decomposition of 9-AnCOOH degradation for: (a) no catalyst, direct photolysis; (b) photocatalysis using a TiO2 NTAs sample; (c) photoelectrocatalytic (PEC) with a
bias potential of 0.5 V (vs. SCE) using a TiO2 NTAs sample; (d) photocatalysis using a (10-cycle deposition) Cu–Zn–S/TiO2 NTAs sample; (e) PEC with a bias potential of 0.5 V
(vs. SCE) using a (10-cycle deposition) Cu–Zn–S/TiO2 NTAs sample. The initial concentration of 2,4-D was 20 mg LÀ1
and the pH value was 5.
T. Tran.T et al. / Chemical Engineering Journal 210 (2012) 425–431 429

7. Author's personal copy
(vs. SCE) using a (10-cycle deposition) Cu–Zn–S/TiO2 NTAs sample.
We find, as expected, photocatalysis (curves b and d) is less effi-
cient at compound degradation than photoelectrocatalytic degra-
dation (curves c and e), while the non-sensitized TiO2 NTAs
samples (curves b and c) are less efficient as a catalyst than the
Cu-Zn-S/TiO2 NTAs samples (curves d and e). The electrochemically
assisted photocatalytic degradation reactions of 2,4-D can be con-
sidered within the context of electrode reactions taking place on
the electrode/liquid interface, with the anodic bias increasing the
separation efficiency of the photogenerated electron-hole pairs
[44]. At all concentration levels the 2,4-D degradation efficiency
of the Cu–Zn–S/TiO2 NTAs samples are superior in performance
than other reported materials including those operating under
UV illumination [45–47]; comparative results are listed in Table 1.
Similar results were obtained in the degradation of 20 mL aque-
ous solution containing 20 mg LÀ1
9-AnCOOH and 0.05 M Na2SO4
aqueous solution at pH = 5 under a 0.5 V bias potential. As shown
in Fig. 6A the peak at 253 nm rapidly decreases, disappearing after
1 h. Fig. 6B shows the 9-AnCOOH removal efficiency for 1 h illumi-
nation where curve (a) shows degradation due to direct photolysis
(25.4%); curve (b) shows PC degradation using a TiO2 NTAs sample
(58.8%); curve (c) shows PEC degradation using a TiO2 NTAs sample
at a bias potential of 0.5 V (vs. SCE) (68.5%); curve (d) shows PC
degradation using a Cu–Zn–S/TiO2 NTAs sample (72.2%); curve
(e) shows PEC degradation using a Cu–Zn–S/TiO2 NTAs sample at
a bias potential of 0.5 V (vs. SCE) (100%).
3.4. Cu–Zn–S sensitized TiO2 NTAs stability
The stability of the Cu–Zn–S/TiO2 NTAs catalyst was evaluated
by repeatedly measuring its efficiency in photoelectrocatalytic deg-
radation of 2,4-D and 9-AnCOOH at a bias potential of 0.5 V (vs.
SCE). Fig. 7A shows the degradation efficiency towards 2,4-D with
2.5 h illumination decreases from 100% on the first run to 94.6%
on the fourth run. The degradation efficiency towards 9-AnCOOH
with 1 h illumination is 100% on the first run decreasing to 95.5%
on the fourth, see Fig. 7B. The Cu–Zn–S/TiO2 NTAs samples were
ultrasonically cleaned in distilled water for 15 min after each use.
4. Conclusions
A new Cu–Zn–S/TiO2 NTAs catalyst was prepared by pulse elec-
trodeposition of Cu–Zn–S ternary nanoparticles onto TiO2 nano-
tube array films. The novel materials were applied to the
photocatalytic degradation of two organic pollutants, 2,4-D and
9-AnCOOH. In comparison non-sensitized TiO2 NTAs samples,
sensitization with Cu–Zn–S nanoparticles results in a significantly
increase in the photocatalytic activity. Moreover, the Cu–Zn–S
nanoparticle sensitized TiO2 NTAs exhibit excellent photoelectro-
catalytic stability.
Acknowledgements
We gratefully acknowledge the National Basic Research Pro-
gram of China (Grants No. 2009CB421601), and the National Sci-
ence Foundation of China (Grant No. 21175038) for financial
support. We thank the editor and reviewers for helpful comments
and suggestions.
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0
20
40
60
80
100
0 20 40 60
Time (min)
0 50 100 150
Time (min)
Removalof9-AnCOOH(%)
0
20
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Removalof2,4-D(%)
First
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(B)
First
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(A)
Fig. 7. Photoelectrocatalytic stability of Cu–Zn–S/TiO2 NTAs on degradation of 20 mg LÀ1
2,4-D solution at pH = 3 after 150 min (A), 20 mg LÀ1
9-AnCOOH solution at pH = 5
after 60 min (B) under AM1.5G illumination.
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